1. Field of the Invention
The present invention relates to a lumber inspection method and device thereof for detecting defective portions due to discoloration which exist in wood-based material such as a veneer or a cut piece cut from a log of wood or the like. For example, for manufacturing plywood, a log is cut using a cutting tool to consecutively obtain veneers with a thickness of several millimeters. The veneers are then cut to a predetermined size, and after drying, several veneers are integrated through lamination using an adhesive. During such manufacturing processes, it is necessary to sort the veneers into those that will compose the outer layers of plywood or, in other words, those with little or no aesthetic defects, and those that will compose the inner layers or, in other words, those with many, albeit nonproblematic, aesthetic defects according to the degrees of positions, numbers, dimensions or the like of defects that affect the quality of the veneer (such as imperfections due to surface discoloration of lumber, warping, holes formed by knots in the veneer having fallen out, and cracks). Such sorting involves classifying into, for example, five to seven grades.
2. Description of the Related Art
Conventionally, the process of sorting veneers into those that will form surface layers of plywood and those that will form inner layers thereof involves naked eye determination by a worker on veneers conveyed through a conveyer.
In addition, a conventional inspection method of defective portions in lumber involves capturing an image of lumber with a color CCD camera, comparing a video signal against reference colors of pitch and discolorations using a color image extraction device and binarizing the video signal, labeling a binarized image matching a measurement object region and contrasting the binarized image with a tolerance value in order to detect defective sites including attached resin such as pitch, rot, and discoloration (refer to Patent Document 1).    Patent Document 1: Japanese Patent Laid-Open No. 09-210785
The conventional techniques described above contain the following problems.
Naked eye determination is inaccurate due to inconsistencies in judgment from person to person and is low in productivity because conveyor speed cannot be increased.
In addition, the conventional method of inspecting defective portions in lumber which involves comparing with a reference color and performing binarization does not include accurate defect inspection using color distribution.
It is an object of the present invention to solve such problems in the prior art and to enable accurate detection of defective portions due to lumber surface discoloration that affect lumber quality using color distribution from a captured image of lumber such as a veneer captured by imaging means even when changes occur in the chromaticity, brightness, and the like of an abnormal portion.